LIGHT-DRIVEN ION TRANSPORT IN BACTERIAL RHODOPSINS

超出所提供的空间。细菌视紫红质是最简单的离子泵，也是普遍存在的七螺旋膜蛋白的结构原型，在过去的几年里，我们确定了七个被捕获的光驱动质子运输系统的光中间体的x射线衍射结构。其余两种状态的结构可间接从非照明突变体中获得。视网膜和视蛋白的构象转换表明这种泵的原子水平机制，但如果没有所有九种中间体的结构，该机制是不完整的。具有较少直接信息的状态是跨膜螺旋的大规模运动介导掩埋水分子的进入和离开的那些状态，所述掩埋水分子影响质子供体和受体的pK并形成质子传导链。这些状态不能被困在三维晶体中。我们将专注于测试和验证的结构，这些关键状态的运输周期的定点自旋标记。大量战略性定位的胱氨酸残基将揭示突变体结构与N、N'和O中间体的对应程度，如果不同，则开始定义这些状态的结构。与此同时，晶体学研究与捕获状态将继续改善现有的结构，并使用可见光和红外光谱，探索仍然悬而未决的问题，质子转移在细胞外区域的蛋白质。这项工作的结果预计将是第一个完整的描述耦合的局部变化在活性位点的蛋白质的全球变化在任何转运蛋白或受体。性能现场=

EXCEED THE SPACE PROVIDED. Bacteriorhodopsin is the simplest of ion pumps, and the structural prototype of the ubiquitous heptahelical membrane proteins, in the last few years we determined the x-ray diffraction structures of seven trapped photointermediates of this light-driven proton transport system. The structures of the remaining two states are available indirectly from non-illuminated mutants. The conformational transformations of the retinal and opsin suggest an atomic level mechanism for this pump, but the mechanism is incomplete without the structures of all nine intermediates. The states with less direct information are those where large-scale motions of the transmembrane helices mediate the entry and exit of buried water molecules that affect the pKs of proton donors and acceptors and form proton conducting chains. These states cannot be trapped in 3-dimensional crystals. We will focus on testing and authenticating the structures of these crucial states of the transport cycle by site-directed spin-labeling. A large number of strategically located cystine residues will reveal how well the mutant structures correspond to the N, N' and O intermediates, and if different, begin to define the strucures of these states. At the same time, crystallographic studies with trapped states will continue to improve the structures already available, and to use visible and infrared spectroscopy to explore still outstanding questions concerning proton transfers in the extracellular region of the protein. The outcome of this work is expected to be the first full description of the coupling of local changes at the active site to global changes of the protein in any transporter or receptor. PERFORMANCE SITE ========================================Section End===========================================